We use tape backups at my job, because we have such a massive amount of data to backup each night. To backup that much to disk would be a huge increase in cost; to maintain long-term backups on disk (our monthly full backups are kept forever) would break the bank.

The best compromise would be to do backup to disk for short-term backups, and backup to tape for long-term backups. But that would still be a lot more expensive than doing all backups to tape.

Another thing to consider is that with tape, you're storing only the storage medium, whereas with drives, you're storing the medium plus the drive, an additional expense. And what is the shelf life of a drive? Tapes have a very long shelf life, if they are kept in the proper type of facility.

You could probably put about 5 TB on a single LTO6 tape (the current standard of LTO tape), depending on the type of data you are storing. You would definitely fill up that tape pretty quickly!

I used to work in our IT department in the 90s and we had a particular model of (reel to reel) tape. Because of the fact that it shed iron oxide everywhere when they were used, I had to ask the data owners of those tapes if we could just scrap them. If they insisted they had to be copied to other (better quality) tapes, then they were only allowed on one particular tape drive, which had to be cleaned when the tape was dismounted. Longevity (in those tapes) wasn't in it. I appreciate that tapes are much better quality nowadays and are in cartridges. For private use, disk is much cheaper though!

I'm blowed if I can remember the name of those tapes - I thought they were etched on my memory!

Ahh it is etched on my memory - they were Memorex Cubic HD tapes. I think they denied there was a problem though, but I believe we got some replacement tapes in the end

Last edited by access-mdb; 2014-05-05 at 13:45.
Reason: memory kicked in

Ya but...how do they verify the backup? I've heard some horror stories on a couple of tech podcasts, the worst of which was a tape backup employed for years; then when they needed it...it had never been backing up correctly from day one. I'm sure there's a way to verify but it must be linear at best eh?

You will see errors occurring when you are making the backups, such as backups failing, tape drives going bad, tapes filling up with too little data on them, etc.

We have never had a failed recovery in the nearly eight years that I have worked here. We have, however, had some bad tapes. The way we knew that they were bad was that we were getting backup failures. Upon further investigation, we found that drives kept going bad. It was determined that bad tapes were causing the drives to go bad. We removed all of the tapes in question from our inventory and replaced all of the bad drives, and we haven't had a problem since.

Our backup software tells us when a backup failed. We then confirm that by checking to see if the index was written to the tape. If the index was written to the tape, then we know that it was a good backup. However, I have seen cases where there was no error message, yet the backup failed. In those cases, I just happened to check a backup, but I had no particular reason to check it, because the backup software showed that it backed up successfully.

We use EMC Networker backup software and Spectralogic backup hardware.

People of today may forget that tape is a 'linear' device:
Tape goes in from one side, comes out from another side.
This shortcoming (slow) is also its strength!

Read and write heads are separate. This is also true for consumer audio tape machines. Hence we have 'tape monitor' function and 'monitor output'.
When the tape goes in, it first passes through the write head. Then before it goes out, it passes through the read head.

With that, you can 'monitor' the condition. First you write to tape. When it then passes through the read head, you get the true output from the written signal on the tape (hence 'monitor').

For audio tape, while recording, you 'simultaneously' also hear the recorded output, right from the tape (from the 'monitor output' if the tape machine has one). No more 'silent run'. That is, you are enjoying the sound while recording. Monitor output feature is usually in premium tape recorders. Later days, almost all have it.

For other hardware types, lengthy and time consuming verification has to be done AFTER the completed backup. And for this to work, the original data has to be there too (to compared to).

Note:
In hard drive, the read/write heads are on a single swing arm, very very close. It cannot write and read at the same time. Even if it is so speedy and able to, the write head strong magnetic field (during write) affects the read capability because they are so close.
On tape recorder, the distance of the read/write head is in inches/multiple inches. In hard drive, it is in micro-inches.

In the latter '90's, tape backup for the home was popular. HDD's weren't all that big (I had a 4GB, which was considered HUGE at the time for a home machine) and portable external drives were more of a concept than a reality. I had a Colorado tape backup system. The cassettes were smaller but thicker than audio cassettes, and the process was slow.

I used it for a year or so, then had a failed backup. I switched to CD's then, and haven't used tape since. Still slow, swapping CD's during backup/recovery. I was a happy camper when writable DVD's were introduced to the home market. I switched to portable external drives when the price point got right and the size of my backups grew.

Create a new drive image before making system changes, in case you need to start over!

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